How to make a Alert Dialog Form Exit Button Click Android Studio

Try To Understands the following java codes for Alert Dialog

public class MainActivity extends AppCompatActivity implements View.OnClickListener { private Button exitbutton; private AlertDialog.Builder alertbuilder; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); exitbutton= (Button) findViewById(R.id.exitId); exitbutton.setOnClickListener(this); } @Override public void onClick(View v) { alertbuilder = new AlertDialog.Builder(MainActivity.this); //for setting Title alertbuilder.setTitle(R.string.title); //for setting Messsage alertbuilder.setMessage(R.string.message); //for Settting Icon alertbuilder.setIcon(R.drawable.sign); alertbuilder.setCancelable(false); alertbuilder.setPositiveButton("YES", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { finish(); } }); alertbuilder.setNegativeButton("NO", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { dialog.cancel(); } }); alertbuilder.setNeutralButton("CANCLE", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { } }); AlertDialog alertDialog=alertbuilder.create(); alertDialog.show(); } }